The present invention relates in general to a method and apparatus for controlling fluid flow with a quarter-turn plug valve with seats operated to lift off the sealing surface of the plug prior to plug rotation and to reseat upon completion of plug rotation. More particularly, the invention relates to a quarter-turn rotary ball valve having a handle operable through a 90xc2x0 angle and having both upstream and downstream seats which are operated to lift off from the sealing surface of the ball prior to initiation of ball rotation and then reseat upon completion of ball rotation.
Certain types of on/off valves have severely attenuated lives due to very concentrated flows with non-axial components during the initial stages of valve opening and final stages of valve closing. In particular, the seats of ball valves and rotary plug valves are susceptible to damage from this type of flow. A second problem which impacts valve actuation is high actuation forces and seat wear due to friction from relative motion of the seats and the sealing plug. This type of problem is common to ball valves, rotary plug valves, and gate valves.
Numerous attempts have been made to overcome these problems for on/off valves. For example, valves have been designed to overcome such problems by reciprocably separating the valve seat(s) from the sealing plug (e.g., a ball, plug, or gate) prior to actually moving the sealing plug and reseating the valve seat(s) onto the sealing plug when the sealing plug reaches its new position. Unseating the valve seat during movement permits a considerable reduction in valve operating force and provides a temporary flow path during operation which is less susceptible to abrasive and cavitational wear than valves with standard, non-reciprocating seats.
U.S. Pat. No. 3,993,136 to Mott discloses a ball valve with lift-off seats configured for operation as a downhole safety valve. This valve operates by means of a linearly reciprocating hydraulic piston concentric with the flow axis of the valve and operating a mechanism which raises the seats from the ball surface prior to rotation and then reseats the valve seats upon completion of rotation. However, this ball valve is unsuitable for operation either manually or by a conventional 90xc2x0 actuator.
U.S. Pat. No. 4,548,384 to Harding discloses a ball valve which has a stationary downstream seat and an eccentrically-mounted ball as a sealing plug. Valve stem rotation causes the valve plug to lift off of the stationary seat due to the eccentricity between the stem and the ball. The opened ball is then reseated by camming into engagement with the upstream seat. The ball only touches one seat at a time, so that trash buildup within the valve is a major problem. In addition, the valve has limited use as it can only seal in one direction.
U.S. Pat. No. 5,179,973 to Dickson et al. discloses another downhole valve operable by a piston reciprocating concentrically with the valve flow axis. This valve causes the ball to lift from its seat due to the applied operating force from the piston during operation when opening, while causing the valve to be pulled against its seat during shifting to its closed position. However, like the Harding valve, it will only hold pressure from one direction.
U.S. Pat. No. 5,005,805 to Morris et al. discloses a tapered plug valve which separates the valve plug from its seats by reciprocably lifting the plug about its rotational axis which is transverse to the valve flow axis. The valve plug is rotated after the plug is lifted, and then the valve plug is reseated after completion of rotation. A stem rotation of more than 90xc2x0 and a special actuator are required to operate this valve. Furthermore, while the transverse reciprocation of the tapered plug causes it to disengage/engage with the seats, the spherical configuration of ball valve sealing surfaces are not compatible with this type of actuation.
U.S. Pat. No. 4,989,641 to Jones et al. discloses a rotary selector valve which uses a Geneva-wheel to move a reciprocable seal out of and into engagement with a sealing port. This device requires a complete turn of its rotational shaft to effect a shifting from one port to another and is not suitable for operation with a conventional 90xc2x0 actuator.
U.S. Pat. No. 4,340,088 to Giesow discloses a downhole safety valve with a partial ball valve sealing plug which is operated by a flow axis axially reciprocable piston. The sealing plug both rotates and reciprocates away from its seat during actuation to the open position. The actuation motion is produced by a lost-motion rack-and-pinion device. This valve is only single seated, so that it only holds pressure from one side.
European Patent EP 0 647 301 B1 to Coufts et al. discloses a ball valve operable by a piston coaxial with the flow axis of the valve. This valve causes the sealing plug to lift off the seat and then rotate during opening. The valve is not reseated in its open position, so trash buildup is likely. Closing reverses the operation. The valve is only seated for holding pressure from one side.
Thus, a need exists for a valve that can seal for pressure from either direction that provides a reduced valve operating force, is less susceptible to abrasive and cavitational wear, and is operable with a conventional 90xc2x0 actuator or manual rotation.
The invention contemplates a valve that preserves the 90xc2x0 actuation rotation of conventional on/off ball valves while providing the separation of the valve seats from the ball sealing plug prior to and following rotation of the valve plug for actuation. The valve of this invention seals for pressure from either direction by using both upstream and downstream seats.
The disclosed valve will reciprocably separate the valve seat(s) from the sealing plug (e.g., a ball or plug) prior to actually moving the sealing plug, move the sealing plug to its new position (a 90xc2x0 rotation for a ball or plug valve), and reseat the valve seat(s) onto the sealing plug. This unseating/reseating of the valve seats is done for both opening and closing operations. The disclosed valve permits a considerable reduction in valve operating force, even under high pressures, and provides a temporary flow path during operation which is less susceptible to abrasive and cavitational wear than standard, non-reciprocating valves.
A preferred embodiment of the invention utilizes a planetary gear train to multiply the rotary actuation shaft motion, while a lost motion coupling between the member driven by the multiplied input shaft motion and the ball permits the driven member to operate a rotary barrel cam to actuate the valve seats prior to ball rotation. Alternatively, any other type of suitable motion-multiplying device, such as shown in U.S. Pat. Nos. 5,312,306 or 5,321,988 and incorporated herein by reference, could be used in place of the planetary gear train.
A preferred embodiment of a quarter-turn has a tubular body having a bore flow passage; a valve element having a through flow passage and two sealing surfaces, the valve element rotatable through a quarter turn about an axis transverse to the through flow passage, wherein the through flow passage is aligned with the bore flow passage to permit flow when the valve element is positioned at a first end of the quarter turn and is misaligned with the bore flow passage to prevent flow when the valve element is at a second end of the quarter turn; an actuating valve stem selectively operable through a quarter-turn input motion for effecting opening or closing of said valve element to permit or prevent flow; motion multiplication means operated by rotation of the actuating valve stem; barrel cam means coaxial with the bore flow passage, the cam means engaging the motion multiplication means whereby motion is transmitted to the cam means through a direct-drive coupling; reciprocable seat means providing a seal with the sealing surfaces when in a first position and separated from the sealing surfaces when in a second position, the seat means forced between the first and second positions by movement of the cam means; and lost motion means interposed between the motion multiplication means and the valve element; whereby rotation of the actuating valve stem initiates movement of the cam means to move the seat means into the second position prior to the valve element rotation and then back into the first position upon completion of the valve rotation.
The disclosed valve has at least the following advantages over existing valves: (a) the preservation of quarter-turn actuation shaft motion, (b) the ability to seal pressure from either direction, (c) the reduction of operating forces, and (d) the reduction of the erosion of the valve ball and seats when the valve is operated under high differential pressures. The preservation of quarter-turn operation is important for compatibility with standard manual valve operating practice and conventional valve actuators. Use of a ball valve in normal industrial service requires that the valve be able to seal for pressures in either direction, as this valve does. The lift-off of the valve seats from the sealing plug greatly reduces the pressure differential across the valve plug, so that the torque necessary to rotate the valve plug is reduced both by eliminating the frictional drag of the valve seats on the plug and by reducing the pressure drop-induced friction of the sealing plug with its rotational journals. These improvements combine to provide a valve suitable for severe operating conditions, including high pressure and abrasive service.